Barbronia weberi (Clitellata, Hirudinida, Salifidae) has ovary cords of the Erpobdella type

Abstract

The organization of the ovaries in representative of the Salifidae (Hirudinida, Erpobdelliformes) was studied at the ultrastructural level for the first time. Like in other leeches, the ovaries of Barbronia weberi are composed of an outer envelope (i.e., an ovisac made up of two coelomic epithelia, muscle cells, and connective tissue) and several internal units, which are broadly similar to the ovary cords found in representatives of the Erpobdellidae. There are usually 6-8 ovary cords that are twisted or cambered with a narrow apical part and a broader, irregularly shaped distal end in each ovisac of B. weberi. Each ovary cord is built from somatic and germ-line cells and the latter tend to form multicellular cysts that are equipped with a central cytoplasmic core (cytophore). There are two morphologically different subpopulations of germ-line cells: oocytes and more numerous nurse cells. Growing oocytes form protuberances on the ovary cord surface and eventually detach from the cord and float freely in the ovisac lumen, whereas the other components of germ-line cysts (i.e., nurse cells and cytophore) degenerate. It should be pointed out that there is a prominent gradient of germ-cell development along the long axis of the cord. The somatic cells form the ovary cord envelope (the so-called spongiosa cells) and also penetrate the spaces between germ-line cells. Both kinds of the somatic cells, that is, those forming the cord envelope and the somatic cells that are associated with oocytes (follicular cells) have a well-developed system of intercellular channels. Additionally, one prominent somatic cell, the apical cell, was found at the apical tip of each ovary cord. Because the aforementioned features of ovary cords found in B. weberi are very similar (with a few minor exceptions) to the ovary cords that have been described in Erpobdella octoculata and E. johanssoni, we propose the term "ovary cords of the Erpobdella type" for them. Our results support a close phylogenetic relationship between Salifidae and Erpobdellidae.